1. Field of the Invention
The invention concerns a furnace to solder integrated circuit chips. More particularly, it concerns a furnace used to solder chips to a hybrid circuit ceramic substrate.
2. Description of the Prior Art
Until now, integrated circuit chips have been soldered only in their packages. For this purpose, the package is placed in a furnace comprising heating resistors. A eutectic preform is placed in the package at the place where the chip has to e soldered. The temperature of the furnace is made to rise until the preform reaches melting temperature. The integrated circuit chip is placed in the package and the heating is stopped. In cooling down, the preform enables the chip to be fixed mechanically to the package. To remove the chip from the package, the same operation is performed to take the preform to its melting temperature.
Hybrid circuits are having to be increasingly used. These hybrid circuits consist of a set of integrated circuits and other components arranged on a single substrate. The chips are usually bonded to the substrate. Now, the technique which consists in bonding the chips is not reliable in the long run. Furthermore, the bonder does not provide for efficient heat dissipation. However, it is impossible to use the technique of eutectic soldering for hybrid circuits because the existing equipment cannot be used, on the one hand, to receive circuits of this type and, on the other hand, to solder all the parts at the same time. Now, if the chips are soldered one after the other, the already positioned preforms reach their melting temperature and the chips get detached as and when they are positioned. Nor is it possible to unsolder any defective chip without disturbing all the other chips.
However, there is a soft soldering technique entailing a passage through a conveyor-fitted furnace. However, the wettability is too poor and is therefore not suitable and, furthermore, the positioning that can be obtained for the circuits is very inadequate.
The present invention makes it possible to cope with all these problems by proposing a furnace comprising a heating frame and a device for the localized supply of heat, this assembly being used to older chips one after another without disturbing already soldered chips.